In this project we plan to characterize the phosphoprotein phosphatases of hepatic glycogen metabolism with regard to the following: 1) their physiological regulation and their roles in mediating the effects of hormones and other metabolic effectors; 2) the physiological significance of their decreased activities in the diabetic liver; 3) their physical chemical properties; and 4) the significance of the association of their activities with specific subcellular organelles such as the smooth endoplasmic reticulum. More specifically, it is envisioned that such investigations will lead to a better understanding of the mechanism of action of insulin at the molecular level. The hypothesis which is being tested is that one of the major actions of insulin on cellular metabolism is to acutely and/or chronically affect the activities of certain phosphoprotein phosphatases of which those affecting glycogen metabolism are a part. A variety of approaches will be utilized to approach these issues. Studies will be carried out using in vivo models, isolated tissues including isolated hepatocytes and hepatocytes in primary cultures from normal and experimentally manipulated animals, and methods of protein chemistry for enzyme isolation and enzyme kinetic analysis.